The invention relates in general to mechanism for controlling the placement of treatment devices within the human body. More specifically, the invention relates to a pullback mechanism for use with in-situ treatment devices including flexible insertion devices that incorporate x-ray emitters.
Restenosis is a heart condition that afflicts 35%-50% of all people who undergo balloon angioplasty to improve blood flow in narrowed sclerotic arteries. The condition consists of a significant re-closing of the treated artery segment hours to several months after the procedure. As a result, the arterial lumen size is decreased and the blood flow downstream from the lesion site is impaired. Consequently, patients afflicted with restenosis must undergo an additional balloon angioplasty, and in some cases a coronary bypass surgery must be performed. Aside from the pain and suffering of these patients, recurrent stenosis is also a serious economic burden on society, with estimated expenses as high as 3.0 billion dollars per year in the United States economy alone.
Attempts to treat restenosis have been concentrated in both the pharmacological and medical device areas. While pharmacological solutions have been proven effective in treating only acute restenosis, a condition developing immediately after balloon angioplasty, some progress has been made with medical devices in the treatment of long term restenosis, a condition that develops up to a few months following balloon angioplasty. An example for such medical device is the stent. Stents can be inserted into an occluded artery to hold it open. Stents have been shown to prevent two of the three mechanisms that cause recurrent stenosis, namely, elastic recoil of the artery and negative remodeling of the arterial structure. The third mechanism, neointimal growth, consists of hyper-proliferation of smooth muscle cells from the lesion into the lumen and is not prevented by stents.
Ionizing radiation holds great promise for treating restenosis. Ionizing radiation serves to damage undesirable hyper-proliferating tissue and ultimately to prevent the hyper-proliferation of smooth muscle cells in the irradiated region. Research has shown that gamma and beta radiation delivered at the location of stenotic lesions effectively stop both animal and human intimal proliferation. The effective, yet non-hazardous, required dose to treat human restenosis is between seven and forty Gray (mjoule/gram), preferably a dosage greater than fifteen Gray measured two mm from the center of the radiation source that penetrates the artery wall at a two mm depth over the lesion length.
In view of the above, various methods have been proposed to provide ionizing radiation treatment. For example, radiation catheters, based on the use of radioactive sources such as beta xe2x88x92emitting 32P, 90Sr/90Y, 188W/188Re, beta+emitting 48V or gamma emitting 192Ir, are at various stages of development and clinical evaluation. The radioactive sources, in a variety of configurations, are introduced to the treatment sites using special radiation catheters and the radioactive source is placed at the treatment site for a predetermined time period as to deliver the proper radiation dose. Radioactive stents are also used as alternative delivery means, incorporating some of the above radioactive isotopes.
An additional approach to providing ionizing radiation treatment is through the use of an x-ray emitting energy transducer that is not radioactive. Co-pending and commonly assigned U.S. patent application Ser. No. 09/325,703 filed Jun. 3, 1999, and U.S. patent application Ser. No. 09/434,958 filed Nov. 5, 1999, describe miniaturized energy transducers that are coupled to flexible insertion devices to permit x-ray radiation treatment within the human body. Use of the miniaturized x-ray emitting energy transducer offers certain advantages with respect to intra vascular gamma and beta sources. These advantages are, but are not limited to, localization of radiation to the treatment site so that the treatment site may be irradiated with minimal damage to surrounding healthy tissue; reduction of hospital personnel risk due to exposure to radioactive materials; and minimization of the regulatory burden and additional costs that arise from the need to comply with nuclear regulatory requirements.
Regardless of the type of treatment device utilized, it is desirable to provide concise control of the placement and movement of the treatment device within the human body, thereby insuring that the treatment area is exposed to the correct dosage of radiation during the in-situ procedure. In cases in which the treatment device is provided as part of a catheter assembly, it has been proposed that a catheter pullback device be utilized to control the location and movement of the treatment device within the human body. International Publication Number WO 99/44687, for example, describes a system for delivering x-ray radiation including a catheter provided with an x-ray emitting device. The location of the catheter is controlled through the use of a reusable, customized pullback mechanism designed to work with a specific catheter device. Conventional pullback mechanisms, however, suffer from a number of disadvantages including: the need to sterilize the devices between procedures or alternatively to use sterile package, difficulties in locating the pullback mechanisms close to the entry point of the catheter due to their bulk and weight, and lack of interchangeability with conventional catheter devices and assemblies.
In view of the above, it is an object of the present invention to provide a pullback mechanism that provides precise location and movement of a treatment device within the human body. It is a further object of the present invention to provide a pullback mechanism of simple and lightweight design that can be easily handled during medical procedures and placed close to the entry point of a catheter. It is also an object of the present invention to provide an inexpensive pullback mechanism that can be disposed of after a procedure, thereby avoiding the problems associated with repeated sterilization or the need for sterile package. Still further, it is an object of the invention to provide a universal pullback mechanism that can be used with a variety of catheter assemblies and devices.
A pullback mechanism is provided that permits precise location and movement of a treatment device within the human body. The pullback mechanism is of simple and lightweight design that can be easily handled and located during medical procedures. Sterilization problems associated with conventional devices are avoided, as the pullback mechanism is disposable and therefore need not be repeatedly sterilized or repeatedly disposed within a sterile package for multiple uses. The pullback mechanism uses retainer mechanisms that can clamp and hold a variety of catheter assemblies and devices.
A pullback mechanism is provided that includes base block, a clamping retainer, and a sliding retainer. The clamping retainer preferably includes a clamping block and a mechanism for tightening the clamping block against the base block. The mechanism for tightening the clamping block against the base block preferably includes a clamping block bolt and a clamping block nut that is threaded over the clamping block bolt. The sliding retainer preferably includes a retainer carriage on which is mounted a clamping retainer and a mechanism for tightening the clamping retainer against the retainer carriage. As in the case of the clamping block, the mechanism for tightening the clamping retainer against the retainer carriage includes a retainer carriage bolt and a retainer carriage nut that is threaded on the retainer carriage bolt. The clamping retainer is coupled to the retainer carriage by a hinged connection, and includes a recess portion through which the retainer carriage bolt passes when the clamping retainer is opened.
In one preferred embodiment, the sliding retainer is mounted on a guide rail that is fixed to the base block. A pullback line attached at one end to the retainer carriage of the sliding retainer and at a second end to a movement imparting mechanism. A control unit controls the operation of the movement imparting mechanism to impart movement to the pullback line.
Additional preferred features include providing at least one of the clamping block and the base block includes a retaining groove and providing at least one of the retainer carriage and the hinged clamping retainer includes a retaining groove.
In addition, a mechanism for biasing the clamping retainer in a desired position can be employed if desired. The mechanism preferably includes a slide block located in a slot provided in the base block and coupled to the bottom of the sliding retainer, and a tension device coupled to the slide block.
In a further embodiment, a lead screw is provided on the base block and the sliding retainer is moveable coupled to the lead screw by via a threaded mounting hole. In this embodiment, a flexible rotary connection is coupled to the lead screw and to a motion imparting mechanism. A control unit is provided to control the operation of the motion imparting mechanism.
Further features and advantages of the invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiments of the invention and the accompanying drawings.